Poorly adjusted vehicle brakes can result in a vehicle out of service condition and can jeopardize human safety. In order to ensure that a vehicle's brakes are properly adjusted, they must be checked at regular time intervals. It is difficult to check the brakes simply by sensing the "feel" of the brake pedal. Under normal braking conditions the brakes may respond in a satisfactory manner, yet under a hard or panic stop the vehicle operator may be unable to stop the vehicle in a desired distance and/or as the vehicle continues to travel in a straight line.
Before checking the brakes, and then making brake adjustments as needed, the vehicle should be parked on a level surface, with the wheels blocked, with the brakes released, and with the engine off.
A standard prior procedure required a mechanic or vehicle operator to manually pull the brake rod to the limit of its brake-on movement, for example by hand or by prying the brake mechanism with a pry bar. The mechanic then measured the distance from the brake assembly's clevis pin to the face of the air chamber, at both the fully retracted and fully extended position of the brake rod. The difference between these measurements is the brake rod's travel or slack. For example, 3/4th inch of travel is considered acceptable, whereas the maximum allowable travel is 11/2 inch.
Since this manual operation of the brake rod requires about 30 foot pounds of unassisted mechanical force, often two people are required, one to step on the vehicle's brake pedal, and the other to measure the travel of the brake rod.
Brake adjustment, or "taking up the brake slack", in order to provide a required amount of brake rod travel, was accomplished by first making sure that the brakes were released, i.e. off. The adjusting bolt on the brake assembly's slack adjuster arm was then turned. More specifically, the spring locking sleeve was depressed, using a wrench. The adjustment bolt was then tightened until solid turning resistance resulted. This resistance condition indicated that the brake linings or pads were touching the brake drum or disk. A running clearance between the linings/pads and the drum/disk was then restored by backing off the adjusting bolt in the range of from about one-quarter to one-half turn.
The primary utility of the present invention resides in a tool for measuring the extent of travel or movement of a vehicle brake rod as the vehicle's brake mechanism is moved between its brake-off and its brake-on positions.
U.S. Pat. Nos. 4,082,165, 4,754,857, 4,796,731 and 4,798,265 describe various construction and arrangements of vehicle brakes, and these patents are incorporated herein by reference for the purpose of illustrating the background of the invention and the general state of the art.
U.S. Pat. Nos. 4,550,460, 4,572,040, 4,625,353, 4,685,164 and 4,864,900 relate to tools for manually operating the actuating mechanism of vehicle brakes. These patents are also incorporated herein by reference for the purpose of illustrating the background of the invention and the general state of the art.
U.S. Pat. No. 4,550,460 describes a two-piece air brake adjustment and measurement tool. A first part of the tool comprises a scale that is attached to the vehicle frame by means of a permanent magnet. The second part of the tool comprises an elongated handle member having an open-faced channel section fixed to one end thereof. In use, one side or the other of the open channel is located over the brake assembly's slack adjustment arm. This arm is then manually rotated, while movement of the arm is visually observed relative to the scale. In this device, distortion is present since the scale is linear, whereas the adjustment arm moves in an arcuate path.
U.S. Pat. No. 4,572,040 describes an elongated brake adjustment tool having an extending arm or pin that is used to manually ascertain the slack adjustment of a brake adjusting mechanism without the need to go beneath the vehicle.
U.S. Pat. No. 4,625,353 describes an elongated brake adjustment tool. A special spanner is removably attachable to one end of the tool by way of a socket wrench driver. This spanner includes a J-shaped hook that enables the tool to grip the brake's crank device. Manual force on the tool results in pivoting of the crank device. The user observes the resulting distance of travel of the crank device.
U.S. Pat. No. 4,685,164 discloses an air brake adjustment tool providing a channel grip member that is shaped for placement over the brake's pivotable slack adjuster. When so positioned, the handle portion of the tool enables manual pivoting of the slack adjuster, thereby enabling the stroke of the brake's piston rod to be measured.
U.S. Pat. No. 4,864,900 discloses an elongated air brake testing and adjustment tool having a forked end that fits over the brake's actuator lever. This patent provides that the brake's clevis is disconnected prior to movement of the actuating lever, this movement being for the purpose of determining if rotation of the actuating lever is excessive.
It is also known that brake adjustment/wear indicators exist in the art.
U.S. Pat. No. 4,757,300 provides an electrical device wherein a switch actuator, such as a permanent magnet, is mounted on the brake's movable air chamber shaft. A sensor is positioned to respond to this shaft moving an excessive distance as the vehicle brakes are actuated.
U.S. Pat. No. 4,776,438 provides a visual brake adjustment indicator having a bracket that is mounted on the vehicle frame so as to extend adjacent to the brake's air cylinder rod and its clevis pin. A movable pointer or digit is provided on the bracket to indicate the maximum allowable distance of travel of the clevis pin as the brakes are actuated. Within this travel distance the brakes are considered to be properly adjusted. U.S. Pat. No. 4,855,712 is also of this general type.
U.S. Pat. No. 4,279,214 provides a visual brake wear indicator wherein a sleeve member is located on the push rod of the brake actuator. Distance graduations are associated with this sleeve member, to allow visual reading of the amount of travel of the push rod. Fixed distance scales attached to the vehicle frame are shown, as are distance scales carried directly by the sleeve member.
U.S. Pat. Nos. 4,945,818, 4,989,537 and 4,991,310 are also of the above mentioned type wherein brake adjustment/wear indication is provided.
Automatic slack adjusters are also known in the art. These mechanical devices automatically adjust the clearance between the brake linings/pads and the brake drums/rotors by sensing the length of the stroke of the air chamber's push rod. More specifically, in these devices the length of the stoke is set at the time the slack adjuster is installed. When the brake linings/pads wear, the above mentioned clearance increases. If the stroke length exceeds a given limit, the slack adjuster automatically makes an adjustment during the return stroke of the push rod. It is general practice to hold a template adjacent to the brake push rod, and to then use a pry bar to move the brake rod to its brake-on position, as movement of the brake rod is observed relative to min/max marks that are carried by the template. From this data, the length of the brake rod stroke when the slack adjuster is initially installed.
The present invention also finds utility for use with such automatic slack adjusters in that the one-piece tool of this invention provides a convenient means whereby one individual can set the length of the brake rod stroke when the slack adjuster is initially installed, and/or to periodically check the length of the brake rod stroke, without the need to use a separate template or movement scale.